Plants perceive light as an important environmental cue. They sense the UV-B part of the solar spectrum through the UVR8 photoreceptor that activates acclimatory responses associated with protection against this potentially damaging radiation. UVR8 enhances the stability of the HY5 transcription factor by inhibiting the activity of COP1, an E3 ubiquitin ligase that targets HY5 for degradation. The teams of Michael Hothorn and of Roman Ulm have now discovered that the UVR8 mechanism of action involves direct competition between active UVR8 and HY5 through interaction domain mimicry and overlapping binding sites on COP1. This mechanism was found to be conserved in other photoreceptor signaling pathways. The study was published in The EMBO Journal on July 15, 2019.